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OSN 500 550 580 V100R008C50 Commissioning and Configuration Guide 02

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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
Basic Concepts

Basic Concepts

This section describes the basic concepts of pulse code modulation (PCM).


Foreign exchange station (FXS) and foreign exchange office (FXO) ports are used for analog telephone lines. They are usually used in pairs, similar to the relationship between a plug and a socket. An FXO port receives the dial tone voltage from an FXS port.

The following describes the positions of FXS and FXO ports, using the connection between a telephone and a telephone company as an example.

  • If a private branch exchange (PBX) is not used, the telephone's FXO port is directly connected to the FXS port provided by the telephone company.

  • If a PBX is used, the FXO port provided by the telephone company is connected to the PBX's FXS port, and the telephone's FXO port is connected to the PBX's FXS port.

A-Law and μ-Law

In non-linear quantization from the magnitude of sampled input signals to quantized output data, two algorithms are available:

  • A-law companding

    A-law companding applies to the digital telephone communication (mainly in Europe and Mainland China). The related mathematical expressions are as follows:

    • Y = (A x X)/(1 + lnA) (0 ≤ X≤ 1/A)
    • Y = (1 + ln(A x X))/(1 + lnA) (1/A ≤ X ≤1)

    In the preceding mathematical expressions, X represents the normalized value of an input signal, and Y represents the signal after companding. A-law uses 13-segment piecewise linear approximation (A = 87.6) for easy implementation on digital circuits.

  • μ-law companding

    μ-law companding applies to digital telephone communication (mainly in North America and Japan). The related mathematical expression is as follows: Y = ln(1 + μ x X)/ln(1 + μ) (0 ≤ X ≤ 1)

    In the preceding mathematical expression, X represents the normalized value of an input signal, and Y represents the signal after companding. In voice signal encoding, μ usually takes the value 255 for a 24 dB improvement in quantization OSNR.


E&M is a trunk and signaling technology commonly used on PBXs. E&M separates the signaling and voice trunks. E&M is also metaphorically called Ear and Mouth, or RecEive and TransMit. An E&M port is usually connected to a PBX, which outputs signals through the M line and receives signals from the E line.


An E&M port can be connected only to a device provided with an E&M port also.

G.703 64 kbit/s Codirectional Services

In 64 kbit/s codirectional services, information (64 kbit/s service signals) and related timing signals (64 KHz and 8 KHz timing signals) are transmitted through a port in the same direction. One balanced cable pair is used for each pair of transmission directions. The three types of signals are transmitted as the same channel of signals.

Boolean Value Remote Access

Multiple Boolean value signals are input using the PCM board that supports the Boolean value remote access function. The combiner inside the PCM board aggregates the Boolean value signals into one signal, and the signal is transmitted to the sink end through the SDH line board/PDH tributary board.

Updated: 2019-01-21

Document ID: EDOC1100020976

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